Polyimides represented by KAPTON (manufactured by Du Pont Co., Ltd.) and VESPEL (manufactured by Du Pont Cp., Ltd.) generally have excellent heat resistance, mechanical properties, chemical resistance, flame retardant properties and electric properties. Therefore, polyimides are widely used as a film to flexible print substrates and electric wire-covering materials, and as a molding material to functional materials for engine surrounding parts and electric and electronic parts in automobile industries or airplane industries. These polyimides, however, have a defect in inferior processing characteristics. The first effect of the defect is as follows. Since the polyimides have no thermoplasticity, they are difficult to be subjected to injection molding or extrusion molding, which molding is used in usual polymers, and they are molded by powder sintering and provided to user by part unit. Therefore, the forms of molded articles are limited and they are very expensive. The second effect thereof is as follows. Since the polyimides are insoluble in most of solvents, when they are used to coating materials or films such as adhesives or the like, they must be formed and processed in the step of polyamic acids and thereafter imidized thermally or chemically.
Further, the polyamic acid, which is a precursor of the polyimide, is easily changed with time in the air and has a possibility such that the capability of a resin of polyamic acid after processing cannot be sufficiently exhibited. At the same time, the imidization reaction is performed with water elimination, and so it is apt to be a cause of formation of voids in films and cracks in molding materials. Until now, many studies on expressing the properties of solubility/infusibility, insolubility fusibility, or solubility/fusibility have been done in order to give the forming processing characteristics to polyimides. However, many polyimides having the characteristics have not been prepared until now.
Accordingly, in the electric and electronic fields and the airplane industry and transportation apparatus fields, the development of polyimides having thermoplasticity, excellent high-temperature fluidity, soluble in solvents, capable of being in various forms such as structure materials films, fiber or varnish, and also having excellent heat resistance, mechanical strength, chemical resistance and electric insulating properties has been desired.
As described above, the first object of the present invention is to provide a novel polyimide and a novel imide oligomer, having thermoplasticity, which is favorable for forming processing, preferably also having solubility in solvents, and to provide their precursors, namely, a polyamic acid and an amic acid oligomer.
The second object of the present invention is to provide a novel polyimide and a novel imide oligomer, having such properties that in the beginning, they have thermoplasticity, which is favorable for forming processing, preferably also have solubility in solvents, and after heat treatment, they have heat resistance, mechanical properties, chemical resistance, flame retardant properties and electric properties, which are comparable to thermosetting polyimides, and to provide their precursors, namely, a polyamic acid and an amic acid oligomer.